An increasing number of technologies require large-scale integration of disparate classes of separately fabricated objects into spatially organized, functional systems. Here we introduce an approach for heterogeneous integration based on kinetically controlled switching between adhesion and release of solid objects to and from an elastomeric stamp. We describe the physics of soft adhesion that govern this process and demonstrate the method by printing objects with a wide range of sizes and shapes, made of single-crystal silicon and GaN, mica, highly ordered pyrolytic graphite, silica and pollen, onto a variety of substrates, even without specially designed surface chemistries or separate adhesive layers. The process is compatible with procedures that use special surface chemistries or adhesive layers to bind objects to their printing targets. Printed p-n junctions and photodiodes fixed directly on highly curved surfaces illustrate some unique device-level capabilities of this approach.
Examples of systems that rely critically on heterogeneous integration range from optoelectronic systems that integrate lasers, lenses and optical fibers with control electronics, to tools for neurological study that involve cells interfaced to arrays of inorganic sensors, to flexible ‘macroelectronic’ circuits and actuators that combine inorganic device components with thin plastic substrates. The most significant challenges associated with realizing these types of system derive from the disparate nature of the materials and the often vastly different techniques needed to process them into devices. As a result, all broadly useful integration strategies begin with independent fabrication of components followed by assembly onto a single device substrate. The present invention addresses a need in the art for a reliable and robust transfer printing process that can assemble disparate components onto a single device substrate.
The present invention encompasses a deterministic, high-speed approach for manipulation and heterogeneous integration that uses kinetically controlled adhesion to elastomeric transfer devices, or stamps, to transfer print solid objects from one substrate to another. This technique provides an important combination of capabilities that is not offered by other assembly methods, such as those based on ‘pick and place’ technologies, wafer bonding, or directed self-assembly.
The method presented herein allows manipulation of arrays of objects based on kinetically controllable adhesion to a viscoelastic stamp in a massively parallel and deterministic manner. The mechanics suggest paths for optimizing the material properties of the stamps in ways that have not been explored in soft lithography or related areas. Even with existing materials, the printing procedure provides robust capabilities for generating microstructured hybrid materials systems and device arrays with applications in optoelectronics, photonics, non-planar fabrication and biotechnology without the use of precision moving parts, applied electric or magnetic fields. The stamp-based methods of the present invention are invaluable tools for handling the building blocks of nano- and other emerging technologies to construct devices based on these technologies.